In contemporary optical systems, an optical fiber interfaces with a discrete element such as an opto-electronic device. The opto-electronic device typically includes a hermetic package having conductive leads for electronic communication with devices external to the package.
During manufacture, single or multiple fiber optic pigtails are typically inserted through ferrules provided in side walls of the package. The end face of each pigtail is then positioned and bonded to a package substrate installed within the package. The body of each pigtail is bonded to the corresponding ferrule to facilitate the hermetic seal of the package.
Higher integration typically requires an increased number of pigtails to be introduced at the package perimeter. Alignment tolerances for ubiquitous single-mode fiber are tight, however the end faces of the fibers must be precisely aligned with internal opto-electronic components, for example, to micrometers.
With reference to the front and top views of FIG. 1A and FIG. 1B respectively, in order to manage fibers in a device, the fibers are commonly arranged into an array on a fiber bench 18. The fiber bench 18 is typically fabricated from silicon and includes an upper frame portion 20A and a lower frame portion 20B. A number of opposed V-grooves 24A, 24B are formed in the upper and lower frame portions 20A, 20B. The V-grooves can be fabricated with a high degree of precision both in terms of position and angular orientation, since photolithographic processes are employed.
Fibers 22A, 22B, 22C are inserted and bonded within the V-grooves 24A, 24B, and the fiber bench 18 is prepared for mounting on a package submount or substrate 16. To effect positioning and alignment of the fiber bench 18 on the package substrate 16, alignment features 26 are provided on the package substrate 10. The alignment features 26 include a registration surface 27 designed to abut a corresponding registration surface 28 on the fiber bench 18.
As explained above, the V-grooves can be formed to within precise tolerances with regard to position and angular orientation. However, formation of the registration surface 28 requires a die saw, or cleaving, operation to be performed. Such an operation is relatively imprecise, both in lateral position, i.e., along the x-axis, and in vertical and horizontal angular orientations. For example, if the cleave is taken to the left or right of the intended target position, then the end faces of the array will be misaligned by that same amount. Similarly, if the cleave is taken at an angle other than that which is intended, then angular misalignment of the array will occur. These variables, in turn, lead to low device yield.
The present invention is directed to an apparatus and method that addresses the limitations of the conventional approach described above. In particular, the present invention is directed to an alignment apparatus and method for positioning and aligning a microbench on a substrate having a registration feature in a manner that eliminates the need for precision die sawing or cleaving. By using a rod of known diameter placed in a partial V-groove, the rod itself can be employed as the registration surface for the bench, providing consistent and accurate alignment results.
According to one aspect, the present invention is directed to a bench registration system for registering a bench with an alignment feature on a substrate. The bench includes an outer wall and a registration groove. A cylindrical rod is mounted in the registration groove such that a portion of the cylindrical rod extends beyond the outer wall of the bench to engage the alignment feature.
In a preferred embodiment, the registration groove comprises a V-groove etched in a silicon-based material, and the cylindrical rod contacts the V-groove at an inner contact point and an outer contact point. The outer wall is positioned at a lateral position between the outer contact point and the outermost registration surface of the cylindrical rod portion.
The bench is preferably sawed or cleaved along the registration groove at a lateral position along the lateral axis between the future location of the outer contact point and the outermost registration surface.
The bench preferably includes an upper frame and a lower frame, wherein the upper and lower frames each include opposed upper and lower registration grooves for housing the rod. The lateral axis of the bench and the longitudinal axis of the registration groove may be perpendicular, or may lie at an acute angle with respect to each other.
In another aspect, the present invention is directed to a method for registering a known position on a bench with an alignment feature. A registration groove is formed in the bench. A cylindrical rod is mounted in the registration groove, a portion of the cylindrical rod extending beyond an outer wall of the bench such that the cylindrical rod engages the alignment feature.